Thin film ferroelectric oxides offer unique physical characteristics potentially superior to diffused waveguides fabricated from bulk ferroelectric materials and could dramatically improve the performance of such integrated optic devices as high speed or low voltage electro-optic modulators for broadband applications at bandwidths greater than 100 GHz for example. An electroptic thin film modulator is described in U.S. Pat. No. 3,944,812.
Polycrystalline ferroelectric oxide materials have considered as high dielectric constant and electro-optic thin film materials. However, ferroelectric thin film materials tend to have exceptional properties along one crystallographic direction or axis and only moderate properties along the other crystal directions or axes. Since polycrystalline ferroelectric thin films considered to-date are comprised of randomly oriented grains, the measured dielectric constant and electro-optic coefficients of these films will be an average of the properties in all directions. Thus, the average dielectric constant and electro-optic coefficient of polycrystalline ferroelectric thin films will be considerably less than those exhibited along the optimum crystal direction or axis of the crystal lattice. Higher electro-optic coefficients enable electro-optic moudlators that operate at lower voltage or higher speeds.
Strontium barium niobate (Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6) where x is greater than 0.25 and less than 0.75 (hereafter SBN) is a ferroelectric material exhibiting excellent dielectric and electro-optic properties which are highest along the c-axis of the tetragonal tungsten bronze crystal lattice as described by Prokhorov et al. in Ferroelectric Crystals for Laser Radiation Control, (Adam Hilger, N.Y., 1990) p. 81. Initial studies of Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6 were carried out on Czochralski-grown single crystals as described by Neurgaonkar et al. in Ferroelectrics 15, 31 (1984).
Potassium niobate (KNbO.sub.3) is a ferroelectric material for electro-optic (EO), nonlinear optic (NLO) and photorefractive applications. The electro-optic figure of merit is 13 picometers/volt which surpasses that of LiNbO.sub.3. In addition, potassium niobate possesses excellent non-linear optical coefficients (d.sub.31 =15 picometer/volt and d.sub.33 =27 picometer/volts)
BaTiO.sub.3 is another ferroelectric oxide material that is an atttactive candidate for thin film integrated optics due to its large elecro-optic coefficient of 1640 pm/V in the a-axis of the crystal lattice.
The realization of an electro-optic modulator utilizing a thin ferroelectric film waveguide that effectively modulates light in a manner that offers potential commercial applications has not been achieved. Stringent requirements of low optical loss (e.g. 1 dB/cm nominally required) and bulk-like electro-optic and non-linear optical coeffficients of the thin film ferroelectric oxide waveguide have not been achieved in an electro-optic modulator.
An object of the present invention is to provide for the first time an electro-optic modulator having an oriented thin ferroelectric film waveguide metalorganic chemical vapor deposited with preferential crystal axis orientation effective to modulate light in response to applied bias or voltage.